1068 THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1951 



lator characteristic, but is applied to the receiver at a fixed (70-megacycle) 

 frequency, so that the receiver discriminator does not enter the measurement 

 except as a fixed gain detector. While the transmitter is being tested as 

 above, the magnitude and phase adjustments of the deviation oscillator 

 load impedances are made as required to meet the desired linearity of devia- 

 tion which is normally 1% over the 10-megacycle range. 



VI. CI Alarm and Control System* 



The operation and maintenance of unattended repeater stations require a 

 flexible and rehable alarm system whose performance is commensurate with 

 the importance of the toll and television program services handled by the 

 TD-2 System. The CI alarm and control system has been developed for this 

 purpose and, as its name implies, it serves two functions. The first is that of 

 transmitting detailed alarm information from unattended repeater stations 

 to the responsible alarm centers. The second function is that of transmitting 

 orders, or remote control signals, from alarm centers to unattended stations. 



The salient features of the CI system may be summarized as follows: 



1. It is a voice-frequency system, thus permitting its use with equal 

 facility on cable pairs, open wire fines, or radio channels (or combina- 

 tions thereof) capable of transmitting a 3000-cycle voice band. 



2. It transmits a maximum of 42 separate alarms or indications from 

 each unattended station to its associated alarm center. 



3. It transmits a maximum of ten remote control orders in the opposite 

 direction, that is, from an alarm center to each unattended station for 

 whose operation it is responsible. 



4. A maximum of twelve unattended stations may be associated with one 

 alarm center. 



A typical section of the TD-2 Radio Relay System is shown in Fig. 4. 

 The alarm center for the section indicated is at Cuyahoga Falls, which in 

 this case, is also a maintenance center. Alarm centers and maintenance 

 centers may be located at any attended central office or repeater station on 

 existing cable and open wire routes. 



Alarm signals are transmitted to the alarm center from the unattended 

 station over a one-way, two-wire circuit as shown in Fig. 20. A four-wire 

 local order circuit is used for voice communication between adjacent main 

 radio stations and the intermediate unattended auxiliary repeater stations. 

 The alarm centers and maintenance centers in that alarm section are also 

 bridged on it. Remote control order signals from the alarm center are of 

 such short duration that they can be transmitted without objectionable 

 interference over one side of this four-wire local order circuit. An express 



* Prepared by C. E. Clutts and G. A. Pullis. 



